CS256583B1 - Process for oxidizing cyclohexane to a mixture comprising cyclohexanone and cyclohexanol - Google Patents

Abstract

The subject of the solution is a method of oxidizing cyclohexane to a mixture containing cyclohexanone and cyclohexanol in the presence of catalysts, preferably compounds of cobalt and/or chromium and/or lithium in one or more reaction stages. is characterized by the amount of oxygen or oxygen-containing gas acting on the reaction mixture formed by cyclohexane and its oxidation products per 1 m3 of the effective volume of the reactor, which ranges from 0.88 to 1.5 kmol/h of oxygen per 1 m3 of the reactor volume. The process achieves an increase in the selectivity of cyclohexane to dicarboxylic acids while maintaining or reducing the selectivity of cyclohexane to cyclohexanone and cyclohexanol by about 0.5% or increasing the performance of the cyclohexane oxidation node in the cyclohexanone production technology.

Description

The invention provides a process for oxidizing cyclohexane to a mixture containing cyclohexanone, cyclohexanol in liquid phase with oxygen and / or an oxygen containing gas, wherein the mixture obtained contains an increased amount of cetines and their esters.

In the cyclohexane oxidation process, in addition to the desired cyclohexanone and cyclohexanol products, a considerable amount of undesired products is formed.

Oxidation of cyclohexane with oxygen and / or oxygen-containing gas in the liquid phase is carried out under conditions whereby the selectivity of cyclohexane to cyclohexanone and cycloliexanol is as high as possible. Reaction parameter values and reactor types and reactor designs for cyclohexane selectivity above 82 wt% are known from the literature.

There is known a process for the oxidation of cyclohexane in three or more reaction stages to which oxygen or an oxygen-containing gas is introduced in an amount such that the entire amount of oxygen has reacted or a gas containing 1-2% by volume is removed from the reactor. Oxygen {Belg. pat. 827/835). An increase in cyclohexane selectivity can also be achieved by adding a certain amount of cyclohexane to each stage of the multistage reaction system, wherein cyclohexane and oxygen-containing gas are metered to each stage in a constant volume ratio. (USSR Pat. 503,846). A modification of this process is the oxidation of cyclohexane in which cyclohexane is fed to stages 2 and 3 in an amount of 5 to 20% of the amount of cyclohexane fed to stage 1, wherein the temperature in each stage is constant or decreasing downstream. By using this process, a 15% reduction in the formation of organic acids is achieved. and oxidation by-products of 30 wt. (USSR Pat. 675,759).

By-products of cyclohexane oxidation are organic mono- and dicarboxylic acids having 1 to 6 carbon atoms, hydroxy acids, aldehyde, ketonic and etheric compounds, C 1 to C 5 alcohols, esters of said acids and alcohols, cyclohexanone condensation products and oxo compounds, cyclic and unaryne hydrocarbons and other organic compounds. The lower boiling components (predominantly MEK) of the mono-carboxylic acids as a dilute aqueous solution, the dicarboxylic acids in the main waste stream containing about 10% water (so-called MEK), are removed from the process of the reaction mixture resulting from the cyclohexane oxidation. alcohols C3 to C6) in the so-called " alcohol moieties and residues from the separation of cyclohexanol from cyclohexanone, in particular the higher boiling condensation products.

However, they are looking for their use as secondary petrochemical raw materials. More promising is the use of a waste stream containing C4 to C6 dicarboxylic acids. MEK for the preparation of polyester polyols as one of the raw materials for the production of rigid polyurethane foams. Since C4 and C6 dicarboxylic acids (adipic, glutaric, succinic) are produced by oxidation of cyclohexane or cyclohexanol, respectively. anhydrous mixture of cyclohexanol and cyclohexanone, the possibility of utilizing the waste stream from cyclohexanone production is very interesting.

For this reason, the process of cyclohexane oxidation has been investigated with the aim of increasing selectivity to dicarboxylic acids at the same or only minor selectivity of cyclohexane to the cyclohexanone / cyclohexanol mixture (by about 0.5% w / w), to the detriment of undesirable by-products. It has been experimentally found that this effect can be achieved by appropriate choice of reaction parameters.

It is an object of the present invention to provide a process for the 0xidation of cyclohexane to a mixture containing cyclohexanone and cyclohexanol in liquid phase with oxygen or oxygen-containing gas in one or more reaction stages at temperatures of 130 to 220 ° C and 0.5 to 1.5 MPa in the presence of catalysts. cobalt and / or chromium and / or lithium compounds. It is characterized in that the reaction mixture present in the reactor consisting of cyclohexane and its oxidation products is treated with air or oxygen-containing gas in an amount of 0.89 to 1.5 kmol / h of oxygen per 1 of ³ effective reaction volume.

The best result in terms of cyclohexane selectivity to a mixture of cyclohexanone, cyclohexanol and dicarboxylic acids is obtained when oxygen or gas containing 1 to 1.1 kmol / h of oxygen per 1 m ^{3 of} effective reactor volume is passed through said reaction mixture. The other reaction parameters are maintained at a level such that the reactor exhaust gas contains not more than 5 vol. oxygen. Unreacted cyclohexane is separated from the resulting reaction mixture, which is recycled to the oxidation process together with fresh cyclebexane, and the resulting mixture is worked up in a known manner. The resulting dicarboxylic acids are removed from the reaction mixture as an aqueous solution containing unwanted by-products from the cyclohexane addition. From this stream, they can be obtained by various processes, or this stream, preferably after its concentration, is used to prepare polyester polyols or so-called polyester polyols. ester oils.

An advantage of the process according to the invention is the use of a cyclohexane oxidation device for the simultaneous preparation of cyclohexanone, cyclohexanol and dicarboxylic acids at the same and the same respectively. slightly reduced selectivity of cyclohexane to a mixture of cyclohexanone and cyclohexanone. A further advantage of the present invention is to increase the cyclobexane oxidation node performance in the production process, cyclohexanone, while respecting and respecting the process. slightly reducing the selectivity of cyclohexane to cyclohexanone and cyclohexanol. The advantage is also the ease of realization and control of the oxidation process with the possibility of using various types of reactors for the oxidation of cyclohexane.

The following examples illustrate the process of the invention:

Example 1 (comparative)

In an oxidation reactor through which cyclohexane and its oxidation products with a catalyst of about 2.5 ppm of cobalt flow, at a temperature of 159-165 ° C and a pressure of 0.9 MPa, air is forced through the reaction volume at 0.87 kmol / h of oxygen in in the form of air per 1 m ^{3 of} effective reactor volume. Under these conditions, the selectivity of cyclohexane to cyclohexanone and cyclohexanol is achieved

The selectivity of cyclohexane to dicarboxylic acids and their esters is 82.5 to 83.5% by weight

3.6 wt.

Example 2

In an oxidation reactor under conditions as in Example 1, the reaction mixture is air-treated at a rate of 1.05 kmol / h oxygen per m ³ effective reactor volume. Under these conditions, the selectivity of cyclohexane to cyclohexanone and cyclohexanol is 82-83.5% and the selectivity of cyclohexane to dicarboxylic acids and esters thereof is 5.2-7.3% by weight.

Example 3

In the oxidation reactor under conditions as in Example 1, air is forced at a rate of 1.2 kmol / h. % of oxygen in the form of air, under these conditions the selectivity of cyclohexane to cyclohexanone and cyclohexanol is 82.5 to 83.0% by weight. and the selectivity of cyclohexane to dicarboxylic acids and their esters from 4.6 to 6.2 wt.

Claims (3)

SUBJECT Process for oxidizing cyclohexane to a mixture containing cyclohexanone and cyclohexanol in liquid phase with oxygen or oxygen-containing gas in one or more reaction stages at temperatures of 130 to 220 ° C and pressures of 0.5 to 1.5 MPa in the presence of a catalyst, preferably cobalt compounds and / or of chromium and / or lithium, characterized in that air and / or an oxygen-containing gas in an amount of 0.89 to 1.5 kmol, preferably 1 to 1.1 kmol of oxygen is passed through the reaction mixture of cyclohexane and its oxidation products. per hour per m ^{3 of} effective reactor volume, the gas leaving the reaction system containing 0 to 5 volume percent oxygen.